[texworks] custom shortcuts

[Jonathan Kew]

For people interested in customizing keyboard shortcuts via an .ini  
file, I have committed Stefan's patch for this to the texworks  
repository. See http://code.google.com/p/texworks/issues/detail?id=17  
for details.

I made one significant change from the original patch: instead of  
requiring you to add a new setting to the main preferences (which  
might be stored in a .plist file [Mac] or the registry [Windows]), it  
will simply look for a file named "shortcuts.ini" in the texworks  
configuration directory, alongside the setup files for syntax  
coloring, auto-indent, etc.

Stefan, sorry this patch has waited so long! I'd still like to  
consider a user interface some day, but for now at least the basic  
functionality is there. Thanks again for all your contributions.

JK